1. Field of the Invention
The present invention relates to an electromagnetic valve driving apparatus, and more particularly to an electromagnetic apparatus for directly driving a valve used in an internal combustion engine, such as an intake valve, in which noises and vibration occurring when the valve is closed or opened are reduced.
2. Description of the Related Art
Electromagnetic apparatus for driving a valve used in an internal combustion engine have been known hitherto, and an example of this kind of apparatus is disclosed in JP-A-7-332044. The apparatus includes an armature fixed to a valve stem at its upper portion, a spring biasing the armature in a valve closing direction, another spring biasing the armature in a valve opening direction and an electromagnetic actuator. The valve is held at a neutral position by both springs when the electromagnetic actuator is not energized. The electromagnetic actuator includes an electromagnet for closing the valve (a closing solenoid) and another electromagnet for opening the valve (an opening solenoid), and it opens or closes the valve by attracting the armature. An example of relation between the valve positions and the valve speed in the conventional apparatus is shown in FIG. 18. To bring the valve from an open position to a closed position, the valve opening solenoid is deenergized, and thereby the valve is moved toward the closed position by the spring biasing the valve toward the closed position. Then, the valve closing solenoid is energized, and thereby the armature is attached to the valve closing solenoid and the valve is brought to the closed position. As shown in the graph at the bottom, the valve speed increases just before the closed position because magnetic force attracting the armature increases as an air gap between the armature and the closing solenoid becomes smaller. Then, the valve sits on the valve seat abruptly at the closed position, thereby generating vibration and noises. The vibration of the valve is detrimental to durability of the valve.
The valve speed at a vicinity of the closed position cannot be controlled in the conventional apparatus, and therefore, the abrupt sitting cannot be avoided.